1. Field of the Invention
The invention relates to the production of chlorine gas for the destruction of undesirable organisms by burning a candle which produces chlorine gas in a self propagating exothermic reaction.
2. Description of the Background
Chemicals having the capacity to disinfect and sanitize are widely used in applications as pesticides to eliminate existing organisms and as a preventative treatment to avoid growth or infestation of unwanted organisms. Chlorine is useful in many such applications because of the broad variety of organisms which can be killed by the introduction of chlorine into their environment. Chlorine can successfully destroy biological warfare agents, including viruses, such as equine encephalomyelitis; bacteria, such as those which cause plague, anthrax and tularemia; and fungi, such as coccidioidomycosis; as well as toxic products expressed by such microorganisms, for example, the botulism toxin expressed by the common Clostridium botulinium bacterium. Chlorine gas can be introduced to liquids such as water and it is often used in this fashion to disinfect swimming pools and to prevent the growth of algae in water cooled systems. Chlorine gas can be delivered to the atmosphere to disinfect a closed space by raising the concentration of chlorine, in the air, to a toxic level.
Chlorine is highly toxic, so its use in the form of the liquified gas (commonly sold in steel cylinders holding 75 pounds or more) presents a significant hazard. For this reason, chlorine is also sold in the form of a concentrated solution of sodium hypochlorite (NaOCl, sometimes called “liquid chlorine” or swimming pool bleach) or as the solid calcium hypochlorite (CaOCl.sub.2, “solid chlorine” or bleaching powder). These substances, which are quite costly relative to liquified chlorine gas, usually contain, respectively, excess sodium hydroxide or calcium oxide. Chlorine in this form is safe to handle but it is adapted for use by introducing it to a liquid.
Another alternative to the use of liquified chlorine gas is to generate chlorine on site by the electrolysis of a concentrated aqueous solution of sodium chloride (NaCl or salt) in a two-compartment electrolytic cell. The production of chlorine electrochemically in large chlorine/caustic plants using complex cells which keep the products from the anode separate from the products of the cathode is a well known art (see Kirk-Othmer's Encyclopedia of Chemical Technology, Third Edition, volume 1, pages 799-865 and volume 8, pages 662-695). Electrolysis is an effective way of producing chlorine gas but the aqueous solution must be prepared and a power source is required to initiate the necessary reaction.
A closed space can be disinfected or pests within the space can be eliminated by filling the space with a toxic gas for a period of time long enough to kill the insect. This method is effective for killing; however, this method generally requires several hours to be effective. Typical of these is the method disclosed by Forbes in the U.S. Pat. No. 4,817,329, in which insects, e.g., termites, are killed by applying a heated gas, such as heated air, to wooden surfaces until the building surfaces are heated to a temperature about 120° F. to 135° F. However, this method, using the described temperatures, is not effective for other organisms such as fungi, and toxic molds, bacteria and viruses. Additionally, this type of work must be done in remote locations where a power source is often not available. The availability of heated chlorine gas would enhance the effectiveness as to other organisms but known methods of generating chlorine gas are not conducive to use in a portable system. The bottled pressurized chlorine gas is dangerous to transport and the apparatus for producing chlorine by electrolysis is cumbersome and requires power.
There remains a need for a more portable means to generate heated chlorine gas, which can be safely and easily transported and which does not require a source of power to operate. A number of prior art patents employ solid chemical candles used to produce oxygen to be breathed in an emergency situation. These generally establish a self propagating exothermic reaction to generate the oxygen. Metal powder is the preferred fuel. Iron, manganese, cobalt, copper and nickel are disclosed as fuel, see Zhang, U.S. Pat. No. 6,264,896 and Kshirsagar, U.S. Pat. No. 6,030,583. Copper oxide and nickel oxides are disclosed as catalysts, see Zhang, U.S. Pat. No. 6,264,896. Chlorates and perchlorates of sodium, lithium and potassium are disclosed as sources of oxygen, see Zhang, U.S. Pat. No. 6,264,896. These prior art patents also vary the composition of layers of pyrotechnic material to alter the product and the rate of production. The concept of the solid chemical candle has advantages which are equally well-suited for generating chlorine gas in the present context. It would be greatly advantageous to adapt the existing concept to provide a solid chemical candle for the production of heated chlorine gas. This would provide a convenient and cost-effective device that can be conveniently stored and quickly carried to the location where it is most needed in case of germ warfare, terrorist attacks in areas that are difficult to reach, etc.